Manganese iron phosphate, method for preparing same, and use thereof

Abstract

The application belongs to the technical field of battery materials, and discloses a long strip flaky ammonium manganese iron phosphate secondary particle and a preparation method thereof. The above-mentioned ammonium manganese iron phosphate is prepared by co-precipitation of divalent iron, divalent manganese and phosphorus source, with a mixed solution of a divalent iron source, a divalent manganese source and an antioxidant as a reaction bottom liquid, and the pH value of the reaction process being controlled to be 2-6. The preparation process is simple in operation and low in cost, and is suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and specifically discloses a precursor material of lithium manganese iron phosphate and a preparation method and application thereof. BACKGROUND

[0002] Compared with traditional batteries, lithium ion batteries have the advantages of high energy density, high voltage, long service life, environmental friendliness, etc., and are widely used in electronic devices, automobiles, aerospace, etc. Lithium iron phosphate is a commonly used positive electrode material of lithium ion batteries, which has many advantages. However, due to the limitation of its structure, when applied to batteries, it has the disadvantages of low electronic conductivity, small lithium ion diffusion coefficient and low material compaction density, which greatly limits the application of lithium iron phosphate. In order to broaden the application of lithium iron phosphate, manganese compounds are introduced into lithium iron phosphate to form a lithium manganese iron phosphate solid solution. Due to the high electrochemical reaction voltage and good electrolyte compatibility of manganese compounds, the lithium manganese iron phosphate solid solution has good capacity and cycle effect. Theoretically, it has a specific capacity of 171mAh / g and a discharge platform of about 4.1V. At the same time, it has the advantages of high safety, good cycle performance and safety and non-toxicity. This also makes lithium manganese iron phosphate become an ideal positive electrode material for new generation of lithium ion power batteries.

[0003] CN115043387A discloses a preparation method of ammonium manganese iron phosphate, lithium manganese iron phosphate and its application. Metal mixed salt solution, ammonium dihydrogen phosphate solution and organic solution are mixed to obtain metal salt mixed solution and phosphate mixed solution. Metal salt mixed solution, phosphate mixed solution and ammonia are added into the bottom liquid to react, and ammonium manganese iron phosphate is obtained by solid-liquid separation. The method controls the reaction pH to be 8-9, and the amount of ammonia and other pH adjusters is large. Moreover, the reaction is carried out in an organic solvent, which not only increases the cost but also is not conducive to washing.

[0004] CN114348982A discloses a preparation method of manganese iron phosphate, lithium manganese iron phosphate, a lithium ion battery and an electrical equipment. Raw materials including iron powder, manganese source and phosphoric acid are mixed to obtain a manganese iron phosphorus solution by solid-liquid separation. The manganese iron phosphorus solution is diluted with water and aged in an inert atmosphere to obtain manganese iron phosphate trihydrate. The method needs acid dissolution, filtration and aging, and has a long process flow, large amount of waste water and complex operation.

[0005] CN115231544A discloses a preparation method of ammonium manganese phosphate and a lithium ion battery positive electrode material. The preparation method of ammonium manganese phosphate includes the following steps: mixing manganese source solution, phosphorus source solution and ammonium source solution, completing aging, and then performing solid-liquid separation to obtain ammonium manganese phosphate. The method does not introduce iron source in the synthesis stage. If iron source is introduced in the subsequent process, the process is complex, and it is difficult to form a homogeneous material.

[0006] CN116675204A discloses a preparation method of a dense type ammonium manganese iron phosphate precursor, a positive electrode material and a battery, and the preparation method of the ammonium manganese iron phosphate comprises the following steps: feeding a phosphorus source, an iron-manganese mixed solution and ammonia water in parallel with pure water as a bottom solution, and finally performing post-treatment to obtain a spherical ammonium manganese iron phosphate with flaky primary particles stacked. SUMMARY

[0007] The purpose of the present application is to provide a manganese iron phosphate material with secondary particles in the form of long and thin flakes and a preparation method and application thereof.

[0008] To achieve the above purpose, the present application provides the following specific technical solutions.

[0009] Firstly, the present application provides a manganese iron phosphate with secondary particles in the form of long and thin flakes.

[0010] In a further preferred embodiment, the tap density of the manganese iron phosphate is 0.5-1.5 g / cm 3 ; and the specific surface area is 1-6 m 2 / g.

[0011] Secondly, the present application provides a preparation method of the above manganese iron phosphate, comprising the following steps:

[0012] (1) dissolving a soluble divalent iron source, a divalent manganese source and an antioxidant in water to obtain a mixed solution;

[0013] (2) feeding a phosphorus source solution and an ammonia water solution into the mixed solution in parallel to perform a reaction; and maintaining the pH value of the reaction system at 2.0-6.0;

[0014] (3) after the reaction is completed, performing solid-liquid separation on the slurry obtained in the reaction, and washing, drying and calcining the obtained solid phase.

[0015] In a further preferred embodiment, the divalent iron source is one or more than two of ferrous sulfate, ferrous nitrate, ferrous chloride, ferrous oxalate and ferrous acetate.

[0016] In a further preferred embodiment, the divalent manganese source is one or more than two of manganese sulfate, manganese nitrate, manganese chloride and manganese carbonate.

[0017] In a further preferred embodiment, the antioxidant is one or more than two of sodium sulfite, ammonium sulfite, 2,6-di-tert-butyl-4-methylphenol (BHT) and ascorbic acid.

[0018] In a further preferred embodiment, the concentration of the divalent iron in the mixed solution is 0.2-1.5 mol / L; the concentration of the divalent manganese is 0.5-2.0 mol / L; and the concentration of the antioxidant is 0.001-0.01 mol / L.

[0019] In a further preferred embodiment, the phosphorus source in the phosphorus source solution is one or more of phosphoric acid, monoammonium phosphate, dihydrogen ammonium phosphate, ammonium dihydrogen phosphate, ammonium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium phosphate.

[0020] In a further preferred embodiment, the concentration of the phosphorus source solution is 2-6 mol / L.

[0021] In a further preferred embodiment, the feeding flow rate of the phosphorus source solution is 100-1200 ml / min.

[0022] In a further preferred embodiment, the concentration of the ammonia solution is 4-12 mol / L, and further preferably 5-10 mol / L.

[0023] In a further preferred embodiment, the temperature of the reaction system is 50-80℃.

[0024] In a further preferred embodiment, the reaction is stirred, and further preferably the stirring speed is 100-1000 rpm.

[0025] In a further preferred embodiment, the calcination temperature is 400-700℃, and the calcination time is 1-6 h.

[0026] Based on the same inventive concept, the present application claims the lithium manganese iron phosphate material prepared from the aforementioned manganese iron phosphate as a raw material.

[0027] In addition, the present application claims a battery comprising the aforementioned lithium manganese iron phosphate material.

[0028] Compared with the prior art, the above one or more technical solutions of the present application can at least achieve one of the following beneficial effects:

[0029] The present application uses divalent iron and divalent manganese metal elements to co-precipitate with a phosphorus source, which is simple to operate, stable in process control, and suitable for industrial production.

[0030] In the present application, the three elements of manganese, iron, and phosphorus can be uniformly co-precipitated, and the chemical composition is close to the design value.

[0031] In the process of preparing manganese iron phosphate, the present application does not need surfactants, organic solvents, etc., and the raw material does not need to be oxidized in advance, and the aging process is also omitted, which has the advantage of low cost.

[0032] The pH value of the synthesized manganese iron phosphate is low, and the amount of pH regulator can be effectively reduced.

[0033] The secondary particles of the prepared manganese iron phosphate are long and thin, the morphology is special, and the dispersibility is good, which is a new product. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The XRD pattern of the precursor material obtained in Example 1.

[0035] Figure 2 The SEM pattern of the precursor material obtained in Example 1.

[0036] Figure 3 The SEM pattern of the precursor material obtained in Comparative Example 1.

[0037] Figure 4 The SEM pattern of the precursor material obtained in Comparative Example 2.

[0038] Figure 5 The SEM pattern of the precursor material obtained in Comparative Example 3.

[0039] Figure 6 The SEM pattern of the precursor material obtained in Comparative Example 4. DETAILED DESCRIPTION

[0040] During the research of the precursor of lithium manganese iron phosphate, the applicant obtained manganese iron phosphate with secondary particles in the form of long and thin strips by changing the preparation process. It was found during the research that the composition of the bottom solution and the pH value of the reaction system have a great influence on the morphology of manganese iron phosphate, which will be embodied in the specific examples and comparative examples.

[0041] Some embodiments provide a manganese iron phosphate, wherein the secondary particles of the manganese iron phosphate are in the form of long and thin strips.

[0042] In some preferred embodiments, the tap density of the manganese iron phosphate is 0.5-1.5 g / cm 3 , and the specific surface area is 1-6 m 2 / g.

[0043] The secondary particles are in the form of long and thin strips, which is a unique morphology of the manganese iron phosphate obtained by the application and is the original creation of the applicant.

[0044] Some embodiments provide a preparation method of the above-mentioned manganese iron phosphate, comprising the following steps:

[0045] (1) dissolving a soluble divalent iron source, a divalent manganese source and an antioxidant in water to obtain a mixed solution;

[0046] (2) using a mixed solution as a base solution, and flowing a phosphorus source solution and an ammonia solution into the base solution to perform a reaction; keeping the pH value of the reaction system at 2.0-6.0;

[0047] (3) after the reaction is completed, performing solid-liquid separation on the slurry obtained in the reaction, and washing, drying, and calcining the obtained solid phase.

[0048] In the process of preparing manganese iron phosphate or other precursor materials by a co-precipitation process, pure water or an alkaline solution is generally selected as a base solution. For example, CN116675204A mentioned in the background art uses pure water as a base solution to obtain a spherical manganese iron phosphate ammonium with flaky primary particles stacked together. The present application takes a different approach, using a mixed solution composed of a divalent iron source, a divalent manganese source, and an antioxidant as a base solution, and keeping the pH value of the reaction system at 2.0-6.0 to obtain a manganese iron phosphate with long and thin secondary particles. The base solution and the pH value are indispensable.

[0049] In some preferred embodiments, the divalent iron source is one or more of ferrous sulfate, ferrous nitrate, ferrous chloride, ferrous oxalate, and ferrous acetate.

[0050] In some preferred embodiments, the divalent manganese source is one or more of manganese sulfate, manganese nitrate, manganese chloride, manganese perchlorate, and manganese carbonate.

[0051] In some preferred embodiments, the antioxidant is one or more of sodium sulfite, ammonium sulfite, BHT, and ascorbic acid.

[0052] In some preferred embodiments, the concentration of the divalent iron in the mixed solution is 0.2-1.5 mol / L; the concentration of the divalent manganese is 0.5-2.0 mol / L; and the concentration of the antioxidant is 0.001-0.01 mol / L.

[0053] In actual operation, the Mn / Fe molar ratio can be controlled by controlling the concentrations of the divalent iron and the divalent manganese in the mixed solution. For example, the Mn / Fe molar ratio can be controlled to be 1.5.

[0054] In some preferred embodiments, the phosphorus source in the phosphorus source solution is one or more of phosphoric acid, monoammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium phosphate.

[0055] In some preferred embodiments, the concentration of the phosphorus source solution is 2-6 mol / L.

[0056] In some preferred embodiments, the feeding flow rate of the phosphorus source solution is 100-1200 ml / min.

[0057] In some preferred embodiments, the concentration of the aqueous ammonia solution is 4-12 mol / L; further preferably 5-10 mol / L.

[0058] In the reaction process of the present application, the aqueous ammonia acts as both a provider of ammonium and a pH regulator.

[0059] In some preferred embodiments, the temperature of the reaction system is 50-80℃. If the temperature is too high, the secondary particles become thick and dense, and the BET decreases; if the temperature is too low, the coprecipitation reaction is incomplete, the Fe and P contents in the supernatant exceed the standard, and the metal ratio of the product is out of control.

[0060] In some preferred embodiments, the reaction is stirred; further preferably, the stirring speed is 100-1000 rpm. Stirring enables the materials in the reaction system to be mixed more fully and uniformly.

[0061] In some preferred embodiments, the calcination temperature is 400-700℃, and the calcination time is 1-6 h. The calcination process affects the phase composition of the product. It is difficult to prepare pure manganese iron phosphate phase if the calcination temperature is too high or too low.

[0062] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present application is not limited to the following specific embodiments.

[0063] Unless otherwise defined, all the professional terms used below have the same meaning as understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present application.

[0064] Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present application can be purchased on the market or can be prepared by existing methods.

[0065] Example 1

[0066] Step S1, preparation of mixed solution:

[0067] Ferrous sulfate, manganese sulfate and ascorbic acid were dissolved in deionized water to prepare a manganese-iron mixed solution. In the manganese-iron mixed solution, the total concentration of manganese and iron metal ions was 1.5 mol / L, the concentration of manganese ions was 0.9 mol / L, the concentration of iron ions was 0.6 mol / L, and the molar concentration of ascorbic acid was 0.0028 mol / L.

[0068] Step S2, preparation of phosphorus source solution:

[0069] Monoammonium phosphate was dissolved in deionized water to prepare a 4.2 mol / L solution.

[0070] Step S3, preparation of aqueous ammonia solution:

[0071] Preparation of 6 mol / L aqueous ammonia solution;

[0072] Step S4, synthesis reaction:

[0073] Take 50 L of manganese-iron mixed solution as the base solution, and stir at a stirring speed of 523 rpm; under the stirring state, pass the phosphorus source solution and the aqueous ammonia solution into the reaction kettle in a parallel flow manner, and control the flow rate of the phosphorus source solution at 200 mL / min; keep the temperature of the reaction system in the reaction kettle at 65°C, and the pH value at 4.5±0.1.

[0074] Stop feeding after 35 L of the phosphorus source solution is fed, to obtain a reaction slurry;

[0075] Step S5:

[0076] Perform solid-liquid separation on the reaction slurry, to obtain a filter cake, wash the filter cake, and centrifuge to remove water;

[0077] Step S6:

[0078] Put the dewatered material into an oven, dry at 120°C for 10 h; then convey to a muffle furnace, and calcine at 400°C for 2 h, to obtain a precursor material.

[0079] Comparative Example 1

[0080] The difference between Comparative Example 1 and Example 1 lies in the synthesis reaction, specifically:

[0081] Step S4, synthesis reaction:

[0082] Take 50 L of deionized water as the base solution, and stir at a stirring speed of 523 rpm; under the stirring state, pass the iron-manganese mixed solution, the phosphorus source solution, and the aqueous ammonia solution into the reaction kettle in a parallel flow manner, and control the flow rate of the phosphorus source solution at 140 mL / min, and the flow rate of the iron-manganese mixed solution at 200 mL / min; keep the temperature of the reaction system in the reaction kettle at 65°C, and the pH value at 4.5±0.1.

[0083] Stop feeding after 50 L of the iron-manganese mixed solution and 35 L of the phosphorus source solution are fed, to obtain a reaction slurry.

[0084] Comparative Example 2

[0085] The difference between Comparative Example 2 and Example 1 lies in the synthesis reaction, specifically:

[0086] Step S4, synthesis reaction:

[0087] The 50L manganese-iron mixed solution was used as the base solution, and stirred at a stirring speed of 523 rpm. The manganese-iron mixed solution and the phosphorus source solution were introduced into the reactor in a parallel flow manner under stirring, the flow rate of the phosphorus source solution was controlled at 140 mL / min, and the flow rate of the manganese-iron mixed solution was 200 mL / min. The temperature of the reaction system in the reactor was maintained at 65°C.

[0088] After the 50L manganese-iron mixed solution and the 35L phosphorus source solution were introduced, the feeding was stopped, and the reaction slurry was obtained.

[0089] Comparative Example 3

[0090] Comparative Example 3 and Example 1 only differ in that, in step S4, the temperature of the reaction system in the reactor was maintained at 65°C, and the pH value was 6.5±0.1 during the synthesis reaction.

[0091] Comparative Example 4

[0092] Comparative Example 4 and Example 1 only differ in that, in step S4, the temperature of the reaction system in the reactor was maintained at 65°C, and the pH value was 1.5±0.1 during the synthesis reaction.

[0093] Example 2

[0094] Step S1, preparation of mixed solution:

[0095] The ferrous nitrate, manganese chloride and sodium sulfite were dissolved in deionized water to prepare a manganese-iron mixed solution. In the manganese-iron mixed solution, the total concentration of manganese and iron metal ions was 1.0 mol / L, the concentration of manganese ions was 0.6 mol / L, the concentration of iron ions was 0.4 mol / L, and the concentration of sodium sulfite was 0.005 mol / L.

[0096] Step S2, preparation of phosphorus source solution:

[0097] The diammonium hydrogen phosphate was dissolved in deionized water to prepare a 5 mol / L solution.

[0098] Step S3, preparation of ammonia solution:

[0099] The 5 mol / L ammonia solution was prepared.

[0100] Step S4, synthesis reaction:

[0101] The 50L manganese-iron mixed solution was used as the base solution, and stirred at a stirring speed of 523 rpm. The manganese-iron mixed solution and the phosphorus source solution were introduced into the reactor in a parallel flow manner under stirring, the flow rate of the phosphorus source solution was controlled at 140 mL / min, and the flow rate of the manganese-iron mixed solution was 200 mL / min. The temperature of the reaction system in the reactor was maintained at 65°C.

[0102] Stop feeding after 20 L of the phosphorus source solution is fed, to obtain a reaction slurry;

[0103] Step S5:

[0104] The reaction slurry is subjected to solid-liquid separation to obtain a filter cake, the filter cake is washed, and the filter cake is centrifuged and dewatered;

[0105] Step S6:

[0106] The dewatered material is placed in an oven, dried at 120℃ for 10 h, and then conveyed to a muffle furnace, calcined at 600℃ for 2 h, to obtain a precursor material.

[0107] Example 3

[0108] Step S1, preparation of a mixed solution:

[0109] Ferrous oxalate, manganese carbonate and ammonium sulfite are dissolved in deionized water to prepare a manganese-iron mixed solution; in the manganese-iron mixed solution, the total concentration of manganese and iron metal ions is 1.25 mol / L, the concentration of manganese ions is 0.75 mol / L, the concentration of iron ions is 0.5 mol / L, and the concentration of ammonium sulfite is 0.01 mol / L;

[0110] Step S2, preparation of a phosphorus source solution:

[0111] Phosphoric acid is dissolved in deionized water to prepare a 6 mol / L solution;

[0112] Step S3, preparation of an ammonia water solution:

[0113] An ammonia water solution of 4 mol / L is prepared;

[0114] Step S4, synthesis reaction:

[0115] Take 50 L of the manganese-iron mixed solution as a base solution, and stir at a stirring speed of 300 rpm; under the stirring state, feed the phosphorus source solution and the ammonia water solution into the reaction kettle in a parallel flow manner, and control the flow rate of the phosphorus source solution at 1200 mL / min; maintain the temperature of the reaction system in the reaction kettle at 50℃, and maintain the pH value at 5.5±0.5.

[0116] Stop feeding after 20.8 L of the phosphorus source solution is fed, to obtain a reaction slurry;

[0117] Step S5:

[0118] The reaction slurry is subjected to solid-liquid separation to obtain a filter cake, the filter cake is washed, and the filter cake is centrifuged and dewatered;

[0119] Step S6:

[0120] The dewatered material is placed in an oven, dried at 120℃ for 10 h, and then conveyed to a muffle furnace, calcined at 700℃ for 2 h, to obtain a precursor material.

[0121] Example 4

[0122] Step S1, mixed solution preparation:

[0123] Ferrous sulfate and manganese sulfate were dissolved in deionized water to prepare a manganese-iron mixed solution; in the manganese-iron mixed solution, the total concentration of manganese and iron metal ions was 1.75 mol / L, the concentration of manganese ions was 1.05 mol / L, the concentration of iron ions was 0.7 mol / L, and the molar concentration of BHT was 0.001 mol / L;

[0124] Step S2, phosphorus source solution preparation:

[0125] Sodium dihydrogen phosphate was dissolved in deionized water to prepare a 4 mol / L solution;

[0126] Step S3, preparation of ammonia solution:

[0127] An 8 mol / L ammonia solution was prepared;

[0128] Step S4, synthesis reaction:

[0129] The 50 L manganese-iron mixed solution was used as the base solution and stirred at a speed of 100 rpm; under stirring, the phosphorus source solution and the ammonia solution were introduced into the reactor in a co-current manner, and the flow rate of the phosphorus source solution was controlled at 100 mL / min; the temperature of the reaction system in the reactor was maintained at 75±5℃, and the pH value was maintained at 5±1.

[0130] After 43.75 L of the phosphorus source solution was introduced, the feeding was stopped, and a reaction slurry was obtained;

[0131] Step S5:

[0132] The reaction slurry was subjected to solid-liquid separation to obtain a filter cake, which was washed and centrifuged to remove water;

[0133] Step S6:

[0134] The dehydrated material was placed in an oven and dried at 120℃ for 10 h; then it was transferred to a muffle furnace and calcined at 500℃ for 6 h to obtain a precursor material.

[0135] Figure 1 The XRD pattern of the precursor material obtained in Example 1 showed that the precursor material was manganese-iron phosphate.

[0136] Figure 2 The SEM image of the precursor material obtained in Example 1 showed that the precursor material was long and thin flake-shaped and had good dispersibility.

[0137] Figure 3The SEM image of the precursor material obtained from the comparative example 1 shows that the precursor material is a high-spherical ball formed by straightly inserting the sheet.

[0138] Figure 4 The SEM image of the precursor material obtained from the comparative example 2 shows that the precursor material is a low-spherical ball formed by obliquely inserting the sheet.

[0139] Figure 5 The SEM image of the precursor material obtained from the comparative example 3 shows that the precursor material is an irregular sheet.

[0140] Figure 6 The SEM image of the precursor material obtained from the comparative example 4 shows that the precursor material is a thick sheet formed by stacking irregular sheets.

[0141] By comparing and analyzing the pH value control of the reactor bottom liquid and the reaction system of the example 1 and the comparative examples 1-4 and the SEM image of the obtained precursor material, it is not difficult to determine that the present application successfully prepares the long and thin sheet-shaped precursor material by selecting the reactor bottom liquid and adjusting the pH value in the reaction process; the long and thin sheet-shaped precursor material cannot be obtained when the reactor bottom liquid is different or the pH value in the reaction process is not in the range of 2-6.

[0142] The tap density and specific surface area of the precursor materials obtained from the example 1-4 and the comparative examples 1-4 are detected by the following methods.

[0143] The tap density is measured by a tap density instrument with a model of BT-313.

[0144] The specific surface area is measured by a specific surface tester with a model of BSD-BET400.

[0145] The detection results are shown in Table 1.

[0146] Table 1

[0147]

[0148] The above only describes the preferred embodiments of the present application, and it should be noted that the ordinary skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing ferric manganese phosphate, characterized in that, Includes the following steps: (1) Dissolve the soluble ferrous iron source, ferrous manganese source, and antioxidant in water to obtain a mixed solution; (2) Using the mixed solution as the base liquid, and introducing phosphorus source solution and ammonia solution, the reaction is carried out; the pH value of the reaction system is maintained at 2.0~6.0; (3) After the reaction is completed, the slurry obtained from the reaction is subjected to solid-liquid separation, and the solid phase is obtained by washing, drying and calcining. The secondary particles of the ferromanganese phosphate are in the form of long, thin flakes; the tap density of the ferromanganese phosphate is 0.5~1.5 g / cm³. 3 Specific surface area is 1~6m² 2 / g.

2. The preparation method according to claim 1, characterized in that, The ferrous iron source is one or more of ferrous sulfate, ferrous nitrate, ferrous chloride, ferrous oxalate, and ferrous acetate; the ferrous manganese source is one or more of manganese sulfate, manganese nitrate, manganese chloride, and manganese carbonate; and the antioxidant is one or more of sodium sulfite, ammonium sulfite, 2,6-di-tert-butyl-4-methylphenol (BHT), and ascorbic acid.

3. The preparation method according to claim 1 or 2, characterized in that, In the mixed solution, the concentration of ferrous iron is 0.2~1.5 mol / L; the concentration of ferrous manganese is 0.5~2.0 mol / L; and the concentration of the antioxidant is 0.001~0.01 mol / L.

4. The preparation method according to claim 1, characterized in that, The phosphorus source in the phosphorus source solution is one or more of the following: phosphoric acid, monoammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium phosphate.

5. The preparation method according to claim 4, characterized in that, The concentration of the phosphorus source solution is 2~6 mol / L.

6. The preparation method according to claim 5, characterized in that, The feed flow rate of the phosphorus source solution is 100~1200 ml / min.

7. The preparation method according to claim 1, characterized in that, The concentration of the ammonia solution is 4~12 mol / L.

8. The preparation method according to claim 1, characterized in that, In step (2), the temperature of the reaction system is 50~80℃.

9. The preparation method according to claim 1, characterized in that, In step (2), the reaction is stirred.

10. The preparation method according to claim 9, characterized in that, The stirring speed is 100~1000 rpm.

11. The preparation method according to claim 1, characterized in that, In step (3), the calcination temperature is 400~700℃.

12. The preparation method according to claim 11, characterized in that, In step (3), the calcination time is 1 to 6 hours.

13. A lithium manganese iron phosphate material, characterized in that, It is prepared using manganese iron phosphate prepared by any one of claims 1-12 as raw material.

14. A battery, characterized in that, Including the lithium manganese iron phosphate material as described in claim 13.

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